U.S. patent application number 11/942262 was filed with the patent office on 2008-05-29 for architecture to communicate with standard hybrid fiber coaxial rf signals over a passive optical network (hfc pon).
This patent application is currently assigned to GENERAL INSTRUMENT CORPORATION. Invention is credited to Shawn M. Esser, Philip Miguelez, Fred Slowik.
Application Number | 20080124083 11/942262 |
Document ID | / |
Family ID | 39463833 |
Filed Date | 2008-05-29 |
United States Patent
Application |
20080124083 |
Kind Code |
A1 |
Esser; Shawn M. ; et
al. |
May 29, 2008 |
Architecture to Communicate with standard Hybrid Fiber Coaxial RF
Signals over a Passive Optical Network (HFC PON)
Abstract
One or more overlay wavelengths are applied to a GPON
architecture to provide sufficient, cost-effective forward
bandwidth per home for targeted, unique narrowcast services to
allow traditional HFC operators to use a PON architecture with
their existing HFC equipment. A separate return path capability
using a separate coaxial cable with RF signals to the GPON may also
be used. This return capability may be provided either by a fiber
optic link or coaxial link from the home.
Inventors: |
Esser; Shawn M.; (Blue Bell,
PA) ; Miguelez; Philip; (Warminster, PA) ;
Slowik; Fred; (Lansdale, PA) |
Correspondence
Address: |
Motorola, Inc.;Law Department
1303 East Algonquin Road, 3rd Floor
Schaumburg
IL
60196
US
|
Assignee: |
GENERAL INSTRUMENT
CORPORATION
Horsham
PA
|
Family ID: |
39463833 |
Appl. No.: |
11/942262 |
Filed: |
November 19, 2007 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60866906 |
Nov 22, 2006 |
|
|
|
Current U.S.
Class: |
398/68 ;
398/66 |
Current CPC
Class: |
H04J 14/0228 20130101;
H04J 14/0232 20130101; H04J 14/0282 20130101; H04J 14/0252
20130101; H04J 14/0226 20130101; H04J 14/0247 20130101 |
Class at
Publication: |
398/68 ;
398/66 |
International
Class: |
H04J 14/00 20060101
H04J014/00 |
Claims
1. A system for communicating over a passive optical network (PON),
comprising: a headend containing: a broadcast transmitter which
transmits broadcast television signals over an optical fiber; a
narrowcast transmitter which transmits narrowcast signals; and a
wave division multiplexer which multiplexes the broadcast
television signals and a narrowcast signals.
2. The system for communicating over a PON of claim 1, wherein the
headend further comprises a return receiver which is configured to
receive return signals from the passive optical network.
3. The system for communicating over a PON of claim 1, further
comprising an optical network termination (ONT) unit which converts
optical signals to electrical signals at an endpoint of the passive
optical network.
4. The system for communicating over a PON of claim 3, wherein the
ONT unit includes an optical transmitter which transmits a return
optical signal over a different optical fiber than provides optical
signals.
5. The system for communicating over a PON of claim 3, wherein the
ONT unit includes an RF transmitter which transmits a return RF
signal over a coaxial cable.
6. The system for communicating over a PON of claim 5, further
comprising a node which includes an optical transmitter which
converts return RF signals to return optical signals for
transmission to the headend.
7. A optical network termination (ONT) unit for use in a passive
optical network (PON) comprising: an optical receiver which
receives optical communications from a headend through an optical
fiber associated with the PON; at least one interface port which
provides for a connection to an external user device; and a return
path which provides a return communication to the headend through a
transmission medium which does not include the optical fiber on
which the optical communications are received from the PON, wherein
an interface port of the at least one interface port provides
communications to a user device from the PON and provides the
return communication to the PON from the user device.
8. The ONT of claim 7, wherein the return path includes an RF
diplexer which receive communications from the PON to the user
device and return communications from the user device to the PON,
and places the return communications in the return path.
9. The ONT of claim 7, wherein the return path includes an optical
transmitter which transmits the return communications to the
headend over a return optical fiber.
10. The ONT of claim 7, wherein the return path includes an RF
transmitter which transmits the return communications over a
coaxial cable.
11. A method of communicating over a passive optical network (PON),
comprising: transmitting broadcast signals to users over an optical
fiber; transmitting narrowcast signals to users over the optical
fiber; and wave division multiplexing the broadcast television
signals and a narrowcast signals prior to being placed on the
optical fiber, wherein the narrowcast signals include QAM modulated
signals.
12. The method of claim 11, further comprising receiving return
signals from an optical network termination (ONT) unit associated
with users which are carried on a different optical fiber than used
to transmit the broadcast and narrowcast signals to the user.
13. The method of claim 12, wherein the return signals are provided
from the user as return optical signals from the ONT.
14. The method of claim 12, wherein the return signals are provided
from the user as RF signals carried over a coaxial cable and
converted to return optical signals at a node in the PON.
Description
[0001] This application claims the benefit of U.S. Provisional Ser.
No. 60/866,906 filed on Nov. 22, 2006, herein incorporated by
reference in its entirety.
BACKGROUND OF THE INVENTION
[0002] Modern cable telecommunications systems are typically built
with a Hybrid Fiber Coaxial (HFC) network topology to deliver
services to residences and businesses. By using Frequency Division
Multiplexing, multiple services on these systems are carried on
Radio Frequency (RF) signals in the 5 MHz to 1000 MHz frequency
band. The HFC topology carries the RF signals in the optical domain
on fiber optic cables between the headend/hub office and the
neighborhood, and then carries the RF signals in the electrical
domain over coaxial cable to and from the home. The fiber optic
signals are converted to and from electrical RF signals in a device
called a fiberoptic "node." In the coaxial portion of the network,
the signal is split to different housing areas and then tapped off
to the individual homes. The RF signals continue to be transported
through the home on coaxial cables and connected to devices in the
home. Due to attenuation in the coaxial cable and split/tap losses,
"RF amplifiers" are used periodically in the coaxial plant to
amplify the electrical signal so they are at an acceptable level to
be received by the devices at the home.
[0003] Information is transported from the headend/hub office to
the home, such as video, voice and internet data, over the HFC
network. Also, information is transported back from the home to the
headend/hub office, such as control signals to order a movie or
internet data to send an email. The HFC network is bi-directional,
meaning that signals are carried on the same network from the
headend/hub office to the home, and from the home to the
headend/hub office. The same coaxial cable actually carries the
signals in both directions. In order to do this, the frequency band
is divided into two sections, "forward path" and "return path", so
there is no interference of signals. The "forward path" or
"downstream" signals, which typically occupy the frequencies from
52 MHz to 1000 MHz, originate in the headend or hub as an optical
signal, travel to the node, are converted to electrical RF in the
node, and then proceed to the home as electrical signals over
coaxial cable. Conversely, the "return path" or "upstream" signals,
which typically occupy the frequencies from 5 MHz to 42 MHz,
originate in the home and travel over the same coaxial cable as the
"forward path" signals. The electrical signals are converted to
optical signals in the node, and continue to the hub or headend
over fiber optic cables.
[0004] The HFC network is capable of carrying multiple types of
services: analog television, digital television, video-on-demand,
high-speed broadband internet data, and telephony. Cable Multiple
System Operators (MSOs) have developed methods of sending these
services over RF signals on the fiber optic and coaxial cables.
Video is transported using standard analog channels which are the
same as over-the-air broadcast television channels, or digital
channels which are usually MPEG2 signal over a QAM channels. The
most common method for carrying data services, telephony services
and sometimes video, is Data-Over-Cable Service Interface
Specification (DOCSIS). In order to transport information on RF
signals, the MSOs have a significant amount of equipment that
converts the services so they can be carried on RF signals.
Examples of this equipment would be Cable Modem Termination Systems
(CMTS), QAM modulators, Upconvertors and Digital Access Controller
(DAC). Also, devices in the home are required to convert the RF
signals to signals that are compatible with television sets,
computers and telephones. Examples of these devices are television
set-top boxes, cable modems and Embedded Multimedia Terminal
Adapter (EMTA). These devices select the appropriate forward path
signals and convert them to usable signals in the home. These same
devices also generate the return path signals to communicate back
to the headend/hub office. MSOs have a significant investment in
the equipment at the home and headend/hub offices that utilize
DOCSIS and similar protocols. They also have a significant network
operation investment to manage this type of network with regards to
maintenance and customer service.
[0005] Today, the MSOs are facing competition from traditional
telecommunication companies. These companies are utilizing new
technologies where fiber optic cables are laid very close to the
home, called Fiber-to-the-Curb (FTTC), or all the way to the home,
called Fiber-to-the-Home (FTTH). With these technologies, many more
services and higher quality can be delivered to the homes, while
also lowering the maintenance cost of the network because the
active components are reduced. A common type of FTTH network is
Passive Optical Network (PON) where no active components exist
between the headend/hub/central office and the home. There are
several types of PON's including Broadband PON (BPON) and
Gigabit-capable PON (GPON) which are actively being deployed by
telecommunication companies in the United States. The technical
standard for the BPON is defined in ITU-T Recommendation G.983 and
for the GPON is defined in ITU-T Recommendation G.984. For the sake
of this disclosure, the GPON will be used as the reference since
this is the latest PON architecture being actively deployed, but
this invention can apply to other forms of PONs.
[0006] FIG. 1 shows a typical architecture for a GPON and FIG. 2
shows a typical ONT for a GPON. As illustrated in FIG. 1, a forward
path of a typical GPON network contains headend 1 with a broadcast
transmitter 4 and optical amplifier 6, and a wave division
MUX/deMUX 8, which provides communication to a 1xn optical coupler
9 at node 10 over optical fiber 3 to couple n homes 12 to the
communication signal. At the home 12, an Optical Network
Termination unit 11 (ONT) converts the optical forward signals via
optical triplexer 14 containing receivers 15 and 17 and transmitter
16. Interface module 13 provides the Ethernet signals to Ethernet
output 19 for internet data, the POTS signals to RJ11 twisted pair
wires 18 for telephone, and broadcast signals to coaxial cable
output 20 for television (if the video overlay is used). In the
return path, the ONT converts the Ethernet input and RJ11 twisted
pair to an optical baseband digital signal. Any television return
signals utilize the Ethernet input. At the headend/hub/central
office, the GPON utilizes the OLT 2 system as the interface between
the PON and network-side.
[0007] Instead of using DOCSIS and similar protocols like an HFC
network, the GPON utilizes baseband digital protocol for forward
path and return path signals. The forward path baseband digital
signals carry internet data, telephony and sometimes television
service by using Internet Protocol (IPTV). The GPON also has an
option for a forward overlay wavelength to provide enhanced
services to the home. Often, the overlay wavelength is at 1550 nm
and delivers video services in the forward path using Frequency
Division Multiplexing just as the HFC network. This overlay
wavelength is shared over many homes, up to 10000. Unlike the HFC
Network though, the only option for return signals on the GPON is
using the baseband digital return signal. Because of the method
that information is transported, the GPON utilizes vastly different
equipment at the home and headend/hub/central office 1 compared to
HFC network.
[0008] MSO's cannot utilize their current methods of transporting
information over a PON, and therefore cannot utilize their current
headend/hub equipment and home devices in this architecture. In
order to compete with the telecommunication companies, MSOs would
like to migrate to FTTH networks, such as GPON, to offer perceived
and real increases in services and quality. MSOs have a very large
investment in DOCSIS and similar equipment at the headend/hub
office and the home, which cannot be utilized in a GPON network.
Also the network management systems for maintenance and customer
service are built around DOCSIS equipment and, therefore, running a
second system in parallel would be costly.
[0009] Technical issues exist for utilizing the MSO's current
infrastructure equipment in a GPON network. For example, the GPON
network cannot provide sufficient, cost-effective forward bandwidth
per home for targeted, unique narrowcast services if they are
transported using the overlay 1550 nm wavelength. To be
cost-effective, the GPON overlay wavelength is split many times and
feeds many homes, up to 10000, with the same signal. This is
acceptable in current GPON deployments because only broadcast video
services are transported on the overlay wavelength, and all
narrowcast services, such as internet data and telephony, are
transported on the baseband digital signal. In order to use their
current infrastructure, the MSO would also transport narrowcast
services using RF signals on the overlay wavelength in the forward
path. But in this scenario, all homes would share the same
narrowcast bandwidth which would severely limit the amount of
unique services available for each home.
[0010] Further, the MSO's current equipment converts information to
be carried over RF signals in the return path. GPON has no option
to carry RF signals in the return path.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] FIG. 1 illustrates an exemplary GPON architecture with
broadcast overlay wavelength.
[0012] FIG. 2 illustrates an exemplary GPON ONT with broadcast
overlay capability.
[0013] FIG. 3 illustrates an exemplary GPON architecture with the
broadcast and narrowcast overlay wavelengths in the forward
path.
[0014] FIG. 4 illustrates an exemplary modified GPON ONT with a
second optical return transmitter.
[0015] FIG. 5 illustrates an exemplary architecture with broadcast
and narrowcast overlay wavelengths and second optical return
signal.
[0016] FIG. 6 illustrates an exemplary modified GPON ONT with a
coaxial return RF signal.
[0017] FIG. 7 illustrates an exemplary architecture with broadcast
and narrowcast overlay wavelengths and electrical coaxial return RF
signal.
[0018] FIG. 8 illustrates an exemplary migration to GPON.
DETAILED DESCRIPTION
[0019] This disclosure utilizes multiple approaches to solve the
above problems. These approaches can be used together or separately
in a network. In one approach a second overlay wavelength is added
to the GPON architecture so it can provide sufficient,
cost-effective forward bandwidth per home for targeted, unique
narrowcast services. The invention may also or alternatively add
return path capability using RF signals to the GPON. This return
capability may be provided either by a fiber optic link or coaxial
link from the home.
[0020] FIG. 3 illustrates an exemplary architecture with the
broadcast and narrowcast overlay wavelengths in the forward path.
In this embodiment, another overlay wavelength is inserted into
each 1550 nm PON port from the optical amplifier in the
headend/hub/central office 1 via narrowcast transmitters 202, which
may be QAM transmitters. This wavelength contains the unique,
targeted narrowcast services and the number of homes sharing this
signal is much smaller, for example, as few as 32 homes, so the
available bandwidth per home is significantly more than provided in
a traditional GPON network. A narrowcast transmitter 202 is used to
generate this second overlay wavelength, which is wave division
multiplexed at MUX/deMUX 8 with a broadcast signal provided by
broadcast transmitter 4 and amplifier 6. A narrowcast transmitter
is generally defined as fiber optic device that transmits only up
to 400 MHz of targeted services delivered on QAM channels, and it
is much less expensive than a broadcast transmitter which requires
much higher performance. The narrowcast overlay wavelength is
offset from the 1550 nm broadcast overlay wavelength so it can be
efficiently combined with the 1550 nm wavelength, but it would
still be passed along with the 1550 nm wavelength through optical
passives in the GPON. A wavelength division multiplexer (WDM) is
used to insert this wavelength with the 1550 nm broadcast at the
headend/hub/central office. ONT 311 provides the broadcast and
narrowcast signals to the user through ports 18, 19 and 20.
[0021] The inventors provide two techniques for transporting RF
signals in the return path. One is to add an analog return
transmitter to the ONT and add a second fiber optic link to the
GPON so return RF signals are transported from the home to the
headend/hub office. Another is to add a coaxial cable link to the
GPON to carry the return RF signals from the home to an optical
node, and then to the headend/hub office.
[0022] FIG. 4 illustrates an exemplary modified GPON ONT with a
second optical return transmitter and FIG. 5 illustrates an
exemplary architecture with broadcast and narrowcast overlay
wavelengths and second optical return signal. The modified GPON
utilizes the coaxial cable in the home for both forward path and
return path signals, which may be the same way it is utilized in a
HFC network. The ONT 411 is modified to include a RF diplexer 172
and second return optical transmitter 171. The RF diplexer 172
splits off the return RF signals (typically from 5 MHz to 42 MHz/65
MHz) coming from the home. By using a pluggable RF diplexer, the
frequency range for the return signals could be changed (for
example, from 5 MHz up to 105 MHz). These RF signals are directed
to an analog transmitter 171 which converts the RF signals from the
electrical to the optical domain. The wavelength of this second
transmitter may be at any wavelength, but most likely 1310 nm or
1550 nm. FIG. 4 shows the modified GPON ONT with a second Optical
Return Transmitter.
[0023] The analog optical return signal is transported from the
home on a second fiber optic cable 31. This is preferred because
the optical passives in the GPON generally cannot handle a second
return wavelength. This optical return signal is combined with
optical return signals from other homes using an optical coupler
512 (i.e. 1.times.32) in node 500. The combined signals then
travels to the headend/hub office 502 and received by a return
analog optical receiver 505 where it is converted to back to an
electrical signal.
[0024] This embodiment may rely on the standard protocols used
today by the MSOs such as DOCSIS, ALOHA, or similar protocols to
allow for proper timing, data collision control, distance ranging
and RF power, as appreciated by those of skill in the art.
[0025] This embodiment combines multiple return optical signals
onto one fiber. The challenge with this is that if two or more
return lasers are transmitting at the same time, noise can be
generated due to non-linear mixing of the two optical carriers.
Also, lasers will typically generate noise if they are not
transmitting data, which would impact the ability of the optical
receiver to detect the return signal from the active home.
Accordingly, in a preferred implementation, the lasers are turned
off if the transmitters are not receiving RF signals from the home,
and turned on when the transmitter receives a RF signal from
devices in the home. By using the timing from the standard
protocols, only one of the lasers in a PON group (32 homes) would
be turned on and transmitting at a frequency at any given time.
[0026] FIG. 6 illustrates an exemplary modified GPON ONT with a
coaxial return RF signal and FIG. 7 illustrates an exemplary
architecture with broadcast and narrowcast overlay wavelengths and
electrical coaxial return RF signal. Just like in FIGS. 4 and 5,
the modified GPON utilizes the coaxial cable in the home for both
forward path and return path signals, which may be the same way it
is utilized in a typical HFC network. The ONT 611 is modified to
include a RF diplexer 172. The RF diplexer splits off the return RF
signals (typically from 5 MHz to 42 MHz/65 MHz) coming from the
home. By using a pluggable RF diplexer, the frequency range for the
return signals could be changed (for example, to 5 MHz to 105 MHz).
The difference with FIGS. 4 and 5, is that the return network is
similar to today's HFC network. These return RF signals are passed
through the ONT 611 to a coaxial cable 512 from the house to the
street. The return signals from the home are combined with return
signals from other homes through electrical RF tap couplers 713.
These combined returned signals eventually feed into an HFC-type
optical node 709. At node 709, the return RF signals are converted
to the optical domain via transmitter 705 and sent to the
headend/hub office 702.
[0027] A variation of this embodiment is to have the RF diplexer
172 external to the ONT 611. This discrete RF diplexer is on the
coaxial cable on the home-side which splits off the return RF
signals. The return RF signals are routed from the ONT 611 on a
coaxial cable that goes to the street.
[0028] Similar to FIGS. 4 and 5, this embodiment may also rely on
the standard protocols used today by the MSOs such as DOCSIS,
ALOHA, or similar protocols to allow for proper timing, data
collision control, distance ranging and RF power, as appreciated by
those of skill in the art.
[0029] FIG. 8 illustrates a migration of an HFC network to GPON.
The embodiments above leave intact the ONT components that handle
the GPON digital baseband signals for forward path and return path.
These are not used in the initial deployment of this proposed
embodiment if all services are using RF signals in the forward and
return path. If these ONT components are left intact, the
architectures outlined above allow a migration to a GPON without a
truck-roll to the home or replacing the ONT. In order to do this,
the GPON OLT 821 is added at the headend/hub office 800 and the
wavelengths are inserted or dropped using a WDM. At the home,
computers are unconnected from the cable modem and connected to the
RJ45 port on the ONT 811 with CAT5 cable. The telephones are
connected to the RJ11 ports on the ONT. For video services, the
set-top box would likely need to be changed to be compatible with
IP over Ethernet. The secondary fiber optic link or coaxial link
used for return RF signals is no longer used but could be left in
place for future bandwidth capability.
[0030] As an extension of the inventions, the ONT components used
for GPON digital baseband signals could be removed for cost
savings. If this is done, the architecture cannot be migrated to a
GPON or other type of PON without replacing the ONT.
[0031] The present invention allows MSOs to largely use their
existing HFC network architecture in a PON architecture. This
allows the MSOs to utilize the benefits of a PON architecture in a
cost effective manner which takes advantage of their investment in
their existing architecture. It also allows the MSO to use familiar
operating and signaling techniques in a PON architecture to
maintain reliability of service which achieving extended bandwidth
to customers.
[0032] Those of skill in the art will appreciate that the above
embodiments may be modified without departing from the sprit of the
invention. For example, the RF signals in the return path may be
carried over medium other than a coaxial cable, such other
communication cables, or even twisted pair.
* * * * *